Metal machining can be accomplished by mounting a workpiece on a rotating chuck of a lathe, and moving the cutting edge of an insert into the workpiece to thread, groove or otherwise remove metal from the workpiece. The insert is mounted on a holder apparatus that is, in turn, mounted on a tool post and adjustable slides of a carriage of the lathe. The cutting edge of the insert has a limited life, and the life of the insert is increased by constructing it with multiple cutting edges. Different machining operations such as cutting different size threads, grooving, etc. require removal of one insert and replacement with another. It would be desirable if the insert had a maximum number of usable identical cutting edges, with the insert being easily repositioned to locate a new cutting edge precisely in the place of a previous one. Also, it would be desirable if one insert could be rapidly removed and another one precisely mounted in its place.